1. Field of the Invention
This invention is directed to telephone control circuits, in general, and to circuits which control the operation of mobile telephones, such as automobile phones, in particular.
2. Prior Art
Mobile telephones have been known in the art for many years. One of the most prominent uses of mobile telephones is in automobiles. In the past, this type of telephone system has not been widely accepted because of the difficulties in setting up the operation thereof. For example, the communications were frequently readily receivable by undesirable reception systems. Moreover, the transmitter for the "calls" was usually fixed and had limited radiation capabilities. Consequently, the phone reception became poor or marginal as the phone instrument moved throughout the geographical area served by the transmitter. However, with the advent of the cellular phone system, the problems of quality of the call tansmission have improved. Consequently, more and more mobile telephones are being installed.
However, in the past, most of the mobile telephones suffered from the lack of "hands-free" operation. This required the phone user to manipulate the instrument with one hand while operating the mobile vehicle, e.g. automobile, with the other hand. This was an undesirable situtation, as well as an unsafe one.
Furthermore, the prior art systems were frequently limited to simplex or one way transmission. Thus, one speaker or user of the phone would have control over the system. By merely continuing to talk, one party could "lock-out" the other party. This was disadvantageous in many cases as well as being annoying or bothersome in other cases.
Consequently, it is highly desirable to have a mobile phone system which is capable of both hands-free and duplex operation.